I was refering to the Dark Side LP that I grew up with And yes, you could look at the Wall as 4 acts...

These are good points. Some artists actually did write "for" the LP format and did clearly think in terms of "side one" and "side two" (or three and four in the case of The Wall).

But here's something interesting:

When Ian Anderson (along with the band Jethro Tull) wrote the masterpiece "Thick as a Brick", it was conceived as one long piece. This was in the days before CDs, so even though they knew full well that it was going to have to be split into two parts, they still thought of it as one long piece. They literally had to "create" a side1->side2 transition moment in the album. If they had done Thick as a Brick today, they might have coded it as one long CD track.